Integrated circuit, non-contact IC card, reader/writer, wireless communications method, and computer program

ABSTRACT

An integrated circuit, a non-contact IC card, a reader/writer, a wireless communications method, and a computer program are provided to improve communication. The integrated circuit configured to execute wireless communication by means of magnetic field. The integrated circuit has a resonance circuit having resonance frequencies of a plurality of levels, a confirmation block configured to confirm whether a predetermined condition is satisfied, and a switching block configured to change the resonance frequencies if the predetermined condition is found satisfied as a result of the confirmation.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2006-163766 filed in the Japan Patent Office on Jun. 13,2006, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an integrated circuit, non-contact ICcard, a reader/writer, a wireless communications method, and a computerprogram.

2. Description of the Related Art

Non-contact IC (Integrated Circuit) cards are widely in use in which anIC chip is embedded in a card to execute wireless communication with areader/writer (R/W) terminal in a noncontact manner. Especially,non-contact IC cards are widely in use in ticket check processing atticket gates of public transportation, payment processing at checkoutcounters of retail stores, and clock-in/clock-out management at offices,for example.

A non-contact IC card contains no power supply. Therefore, thenon-contact IC card uses, as its power supply, a voltage that isgenerated when the IC card is held over a reader/writer terminal throughan antenna coil that receives a magnetic field generated by thereader/writer terminal. The voltage generated as an induced voltage issupplied to each component of the IC card as the power. The non-contactIC card and the reader/writer terminal are communicating each other byuse of the radio wave of a predetermined frequency. The non-contact ICcard and the reader/writer terminal each have a frequency resonancecircuit that resonates at that predetermined frequency. For example, inthe ISO14443 standard that is the communications standard of thenon-contact IC card, the resonance frequency is set to 13.56 MHz.

The response from the non-contact IC card or the IC chip embedded in aportable information processing terminal is supported by “loadmodulation”. In load modulation, the load inside the IC chip is turnedon/off to change the impedance of the IC chip relative to thereader/writer terminal. The reader/writer terminal detects the change inthe power consumption of the IC chip as a voltage change of the carrier(the card or the portable terminal). Therefore, the reader/writerterminal can recognize a response from the IC chip by the occurrence ofa voltage change.

Recently, a method is known in which an IC chip is incorporated in notonly a non-contact IC card but also a portable information processingterminal, such as a mobile phone, and this terminal is held over areader/writer terminal, thereby executing wireless communication withthe reader/writer terminal. Holding such a portable terminal over areader/writer terminal connected to a ticket check system of publictransportation or a register machine at a retail store allows theexecution of ticket check processing or payment processing by use of aportable information processing terminal. Especially, at ticket gates orcheckout counters, it is required to execute communication at highspeeds so as not to put the users of portable information processingterminals into a waiting line. For this purpose, a technology forstabilizing the response from the IC chip is disclosed.

The above-mentioned technology is disclosed in Japanese Patent Laid-openNo. 2001-222696 (Patent document 1). Patent document 1 discloses amethod in which the capacities of capacitors in a resonance circuit in anon-contact IC card is changed to shift the resonance frequency of theresonance circuit, thereby improving the response from the IC card.

SUMMARY OF THE INVENTION

However, it sometimes occurs that the communication between thereader/writer connected to a ticket checking system or a checkoutcounter system and the IC chip embedded in an IC card or a portableinformation processing terminal cannot be successfully executed. Thisunsuccessful communication is mainly caused by ASK (Amplitude ShiftKeying), which is a communication scheme used between the reader/writerterminal and the IC chip. To be more specific, the above-mentioned loadmodulation is used for the response from the IC chip embedded in anon-contact IC card or a portable information processing terminal to thereader/writer terminal and the reader/writer terminal detects the changein power consumption of the IC chip as a voltage change of the carrier(the card or the portable terminal).

In load modulation, the resistor is turned on/off in the IC chip togenerate a diamagnetic field toward the reader/writer terminal thatgenerates radio waves, thereby making a response to the reader/writerterminal. When the impedance of the IC chip relative to thereader/writer terminal changes, the reader/writer terminal can recognizea response from the IC chip. However, depending on the distance betweenthe reader/writer terminal and the IC chip and the diamagnetic fieldgenerated by the turning on/off of the resistor, too, the absolute valueof the impedance including the IC card or the information processingterminal as seen from the antenna of the reader/writer terminal may notchange by varying the load of the IC chip. Hence, in that distance, aresponse from the IC chip may not be recognized by the reader/writerterminal as a response.

Referring to FIG. 9, there is shown a circuit diagram for describingrelated-art reader-writer terminal and IC card. A reader/writer 10 ismade up of a power supply 11, resistors 12 and 13, a capacitor 14, andan antenna coil 15. An IC card 20 is made up of a switch 21, a resistor23, a capacitor 24, and an antenna coil 25. The antenna coil 15 of thereader/writer 10 and the antenna coil 25 of the IC card 20 wirelesslycommunicate each other by use of magnetic field M in a noncontactmanner. Communication by the IC card 20 is executed by changing themagnetic field from the IC card 20 by turning on/off the switch 21.

FIG. 10 is a graph indicative of a problem that the reader/writer alsocannot recognize a response depending on the diamagnetic field caused byturning on/off the resistor. In the figure, the horizontal axis isindicative of the distance between the reader/writer and the IC cardhaving an IC chip and the vertical axis is indicative of voltage V_(R/W)across the antenna of the reader/writer. The relationship betweendistance and voltage with the switch 21 of the IC card 20 being off isindicated by a solid line, while the relationship between distance andvoltage with the switch 21 of the IC card 20 being on. When the switch21 is turned on, the resistor 23 goes valid, upon which a current flowsinto the IC card 20. When the current flows into the IC card 20, thiscurrent causes the antenna coil 25 to generate a magnetic field (or adiamagnetic field). When this magnetic field is received by the antennacoil 15 of the reader/writer 10, a current due to this magnetic field isgenerated on the antenna coil 15, the generated current changing voltageV_(R/W) across the antenna of the reader/writer 10. This change ofvoltage V_(R/W) tells the reader/writer 10 whether there has been aresponse from the IC card 20.

However, depending on the distance between the reader/writer 10 and theIC card 20, there is a position at which turning on the switch 21 on theIC chip side to validate the resistor 23 does not change voltage V_(R/W)across the antenna of the reader/writer 10. In FIG. 10, at a point wherethe solid line and the dashed line cross each other, turning on/off theswitch 21 does not change voltage V_(R/W) across the antenna of thereader/writer 10. Hence a problem that, depending on the distancebetween the reader/writer 10 and the IC card 20, turning on the switch21 by the IC card 20 to validate the resistor 23 may not cause thereader/writer 10 to recognize a response from the IC card 20.

Thus, there is a point at which communication is disabled depending onthe distance from the reader/writer in a response made by turning on/offthe resistor as described above, thereby presenting a problem that aresponse from the IC chip cannot recognized by the reader/writer.Especially, at ticket gates of public transportation and checkoutcounters of retail stores, it is required to execute the communicationas quickly as possible to prevent the users of IC cards from putting ina waiting line. Otherwise, it takes long enough for delaying theprocessing of the passing of the users through these checkpoints,thereby causing inconvenience to the users.

Therefore, the present invention addresses the above-identified andother problems associated with related-art methods and apparatuses andsolves the addressed problems by providing an integrated circuit, anon-contact IC card, a reader/writer, a wireless communications method,and a computer program that are novel and improved.

In carrying out the invention and according to one embodiment thereof,there is provided an integrated circuit configured to execute wirelesscommunication by use of a magnetic field. This integrated circuit has aresonance circuit having resonance frequencies of a plurality of levels;a confirmation block configured to confirm whether a predeterminedcondition is satisfied; and a switching block configured to change theresonance frequencies if the predetermined condition is found satisfiedas a result of the confirmation.

According to the above-mentioned novel configuration, the resonancecircuit provides resonance frequencies of a plurality of levels, andconfirmation block confirms whether a predetermined condition issatisfied, and the switching block switches between the resonancefrequencies of the resonance circuit if the predetermined condition isfound satisfied. Consequently, the above-mentioned integrated circuitpracticed as one embodiment of the invention can change the resonancefrequencies of the resonance circuit to make a response to radio wavestransmitted from the outside.

The above-mentioned predetermined condition may be a predetermined countexecuted in the confirmation block or a predetermined period of timemeasured in the confirmation block. According to this novelconfiguration, the confirmation block counts a predetermined number oftimes and/or a predetermined period of time. As a result, if thepredetermined number of times and/or the predetermined period of time isfound exceeded or passed, the resonance frequencies of the resonancecircuit are switched to make a response to radio waves transmitted fromthe outside.

The above-mentioned integrated circuit further has a capacitor havingcapacitances of a plurality of levels and the switching block switchesbetween the capacitances to change the resonance frequencies. Accordingto this novel configuration, the capacitor has capacitances of aplurality of levels, which are switched to change the resonancefrequencies of the resonance circuit. As a result, switching between thecapacitances of the capacitor can change the resonance frequencies ofthe resonance circuit to make a response to radio waves transmitted fromthe outside.

The above-mentioned integrated circuit further has an inductor havinginductances of a plurality of levels and the switching block switchesbetween the inductances to change the resonance frequencies. Accordingto this novel configuration, the inductor has inductances of a pluralityof levels, which are switched to change the resonance frequencies of theresonance circuit. As a result, switching between the inductanceschanges the resonance frequencies of the resonance circuit to make aresponse to radio waves transmitted from the outside.

In carrying out the invention and according to another embodimentthereof, there is provided a non-contact IC card having theabove-mentioned integrated circuit.

According to this novel configuration, a resonance circuit has resonancefrequencies of a plurality of levels; a confirmation block confirmswhether a predetermined condition is satisfied; and a switching blockchanges the resonance frequencies if the predetermined condition isfound satisfied as a result of the confirmation. As a result, thisnon-contact IC card can change the resonance frequencies of theresonance circuit to make a response to radio waves transmitted from theoutside.

In carrying out the invention and according to still another embodimentthereof, there is provided an information processing terminal having anintegrated circuit.

According to this novel configuration, a resonance circuit has resonancefrequencies of a plurality of levels; a confirmation block confirmswhether a predetermined condition is satisfied; and a switching blockchanges the resonance frequencies if the predetermined condition isfound satisfied as a result of the confirmation. As a result, thisinformation processing terminal can change the resonance frequencies ofthe resonance circuit to make a response to radio waves transmitted fromthe outside.

In carrying out the invention and according to yet another embodimentthereof, there is provided a card reader/writer having an integratedcircuit.

According to this novel configuration, a resonance circuit has resonancefrequencies of a plurality of levels; a confirmation block confirmswhether a predetermined condition is satisfied; and a switching blockchanges the resonance frequencies if the predetermined condition isfound satisfied as a result of the confirmation. As a result, this cardreader/writer can change the resonance frequencies of the resonancecircuit to make a response to radio waves transmitted from the outside.

In carrying out the invention and according to a different embodimentthereof, there is provided a wireless communications method based on anintegrated circuit having a resonance circuit having resonancefrequencies of a plurality of levels. This method has the steps of:confirming whether a predetermined conditions is satisfied; and changingthe resonance frequencies by switching between the resonance frequenciesif the predetermined condition is found satisfied.

According to this method, whether a predetermined condition is satisfiedor not is determined in the confirmation step and, if the predeterminedconditions is found satisfied, then the resonance frequencies of theresonance circuit are changed. As a result, this wireless communicationsmethod can change the resonance frequencies of the resonance circuit tomake a response to radio waves transmitted from the outside.

In carrying out the invention and according to a still differentembodiment thereof, there is provided a computer program configured tocontrol an integrated circuit having resonance frequencies of aplurality of levels. This computer program has the processes ofconfirming whether a predetermined conditions is satisfied; and changingthe resonance frequencies by switching between the resonance frequenciesif the predetermined condition is found satisfied.

According to this computer program, whether a predetermined condition issatisfied or not is determined in the confirmation step and, if thepredetermined conditions is found satisfied, then the resonancefrequencies of the resonance circuit are changed at the resonancefrequencies changing process. As a result, this computer program canchange the resonance frequencies of the resonance circuit to make aresponse to radio waves transmitted from the outside.

As described and according to the invention, an integrated circuit, anon-contact IC card, a reader/writer, a wireless communications method,and a computer program can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating an integrated circuit practicedas a first embodiment of the invention;

FIG. 2 is a circuit diagram illustrating the integrated circuitpracticed as the first embodiment of the invention;

FIG. 3 is a block diagram illustrating an exemplary configuration of anon-contact IC card based on the above-mentioned integrated circuitpracticed as the first embodiment of the invention;

FIG. 4A is a flowchart indicative of a wireless communications methodpracticed as the first embodiment of the invention;

FIG. 4B is another flowchart indicative of the wireless communicationsmethod practiced as the first embodiment of the invention;

FIGS. 5A, 5B, 5C, and 5D are diagrams illustrating relationships betweenthe capacitance of a non-contact IC card and the voltage of areader/writer (R/W);

FIG. 6 is a circuit diagram illustrating an integrated circuit practicedas a second embodiment of the invention;

FIG. 7 is a block diagram illustrating an exemplary configuration of areader/writer terminal practiced as a third embodiment of the invention;

FIG. 8 is a flowchart indicative of a wireless communications methodpracticed as a third embodiment of the invention;

FIG. 9 is a circuit diagram illustrating a circuit of related-artreader/writer terminal aid IC card; and

FIGS. 10A and 10B are diagrams illustrating relationships between thedistance between related-art reader/writer terminal and IC card and thevoltage that occurs on the reader/writer terminal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention will be described in further detail by way of embodimentsthereof with reference to the accompanying drawings. It should be notedthat, throughout the description herein and the drawings accompanyinghereto, components having substantially the same functionalconfiguration are denoted by the same reference numeral, therebyskipping the duplicate description.

A First Embodiment

Now, referring to FIGS. 1 and 2, there are shown integrated circuitspracticed as a first embodiment of the invention. The followingdescribes exemplary configurations of these integrated circuits.

As shown in FIG. 1, an integrated circuit 124 practiced as the firstembodiment of the invention is made up of an antenna coil 102, a firstcapacitor 104, a second capacitor 106, a resistor 107, and a switchingblock 112.

Receiving a radio wave containing a predetermined frequency componentfrom a radio wave generating device, such as a reader/writer terminal,the antenna coil 102 generates an alternate voltage across the antennacoil 102 by electromagnetic induction. In the present embodiment, thenumber of windings of the 102 is three; however, the number of windingsis not limited to three in the present embodiment.

Connecting the antenna coil 102 with the first capacitor 104 in parallelas shown in FIG. 1 configures a resonance circuit. When a change occurson the magnetic field passing the antenna coil 102, an alternate voltageis generated on the antenna coil 102, upon which a current flows intothe integrated circuit 124 through the resistor 107, an electric powerbeing consumed by the resistor 107.

The switching block 112 is used to connect or disconnect the secondcapacitor 106 to or from the integrated circuit 124 by on/offoperations. Connecting or disconnecting the second capacitor 106 to orfrom the integrated circuit 124 causes the resonance frequency of theresonance circuit made up of the antenna coil 102 and the firstcapacitor 104 to change.

The switching block 112 may be formed by a switching element. For thisswitching element, a FET (Field Effect Transistor), a MOSFET (MetalOxide Semiconductor FET) for example, may be used.

FIG. 2 illustrates a status to be obtained after the switching block 112of the integrated circuit 124 shown in FIG. 1 is turned on. When theswitching block 112 is operated to be turned on, the second capacitor106 is connected to the integrated circuit 124 to become valid. Hence,two capacitors, the first capacitor 104 and the second capacitor 106,configure the resonance circuit, thereby changing the resonancefrequency of the resonance circuit. Then, the resonance circuit can passonly the signal having the changed resonance frequency. The passedsignal is passed to a detector, not shown, arranged at a later stage ofthe integrated circuit 124 to be rectified and smoothed.

Changing the capacitance of the integrated circuit 124 to change theresonance frequency causes a change in the impedance of the integratedcircuit 124 as a whole. Use of this impedance change allows the radiowave generating device, such as a reader/writer terminal, determinewhether a response has been made by the integrated circuit 124 to thereception of radio wave. Therefore, incorporating such an integratedcircuit into an information processing terminal, such as a non-contactIC card or a mobile phone that executes wireless communication with areader/writer terminal in a noncontact manner allows the improvement ofthe response to the reader/writer terminal that has outputted radiowaves.

It should be noted that, in the present embodiment, the capacitance ofthe entire capacity is changed by switching between validity andinvalidity of the second capacitor 106 to connect the first capacitor104 and the second capacitor 106 in parallel; however, the presentinvention is not limited to this configuration. For example, thecapacitance of the entire capacitor may be changed by switching betweenthe validity and invalidity of the second capacitor 106 to connect thefirst capacitor 104 and the second capacitor 106 in series.

Thus the integrate circuit associated with the first embodiment of theinvention has been described with reference to FIGS. 1 and 2. Thefollowing describes an exemplary configuration of a non-contact IC cardbased on the integrated circuit associated with the first embodiment ofthe invention with reference to FIG. 3.

Referring to FIG. 3, there is shown a block diagram of an exemplaryconfiguration of the non-contact IC card based on the above-mentionedintegrated circuit.

As shown in FIG. 3, a non-contact IC card 100 is made up of an antennacoil 102, a first capacitor 104, a second capacitor 106, a switchingblock 112, a rectifier 114, a voltage detector 116, a demodulator 118, adigital circuit 120, a memory 122, and a confirmation block 123. Areader/writer 150 is connected to an antenna coil 152.

The non-contact IC card 100 and the reader/writer 150 transmit andreceive radio waves containing a predetermined frequency componentthrough the antenna coil 102 and the antenna coil 152. When the antennacoil 102 receives a radio wave from the antenna coil 152 of thereader/writer 150, an alternating voltage is generated across theantenna coil 102. In the present embodiment, the number of windings ofthe antenna coil 102 is, but not exclusively, three.

The antenna coil 102, the first capacitor 104, and the second capacitor106 make up a frequency resonance circuit. The frequency resonancecircuit is used to pass a particular frequency band (or resonancefrequency) component.

The switching block 112 may be configured by a plurality of switchingelements. Each switching element may be a FET, a MOSFET for example. Inthe present embodiment, the switching block 112 is made up of switches112 a and 112 b.

Operating the switching block 112 to validate the second capacitorallows the switching of the capacitance made up of the first capacitor104 and the second capacitor 106. The resonance frequency is determinedby the inductance of the antenna coil 102 and the capacitance of thefirst capacitor 104 and the second capacitor 106.

The frequency of the radio wave to be transmitted from the reader/writer150 is specified by a communications standard used. For example, withone of the communications standards for the non-contact IC card,ISO14443, the frequency of the radio wave to be transmitted from thereader/writer 150 is specified to 13.56 MHz. The inductance of theantenna coil 102 and the capacitance of the first capacitor 104 areadjusted so as to set the resonance frequency of the frequency resonancecircuit also to 13.56 MHz. It should be noted that the resonancefrequency of the frequency resonance circuit according to the inventionis not limited to 13.56 MHz prescribed in ISO14443.

The resistor 107 is used to consume the electrical power caused by acurrent generated on the antenna coil 102. The non-contact IC card 100consumes the electrical power at the resistor 107, namely, flows thecurrent through the antenna coil 102 to generate a magnetic fieldtherefrom, thereby making a response to the reader/writer 150 throughthe generated magnetic field.

The rectifier 114 is used to convert the alternating voltage generatedin the antenna coil 102 into a direct voltage. The direct voltageoutputted from the rectifier 114 may be used as a power voltage to driveeach component in the non-contact IC card 100. The voltage detector 116detects a voltage value of the direct voltage obtained by the rectifier114. When a voltage value is generated in excess of a predeterminedlevel, the voltage detector 116 stops the operation of the non-contactIC card 100.

The demodulator 118 separates the information from the radio wavetransmitted from the reader/writer 150. The separated information isstored in the memory 122 via the digital circuit 120.

The confirmation block 123 makes a confirmation, when making a responseto the reader/writer 150, whether a predetermined condition is satisfiedor not. If a predetermined condition is found satisfied, then theconfirmation block 123 causes the digital circuit 120 to output a signalfor connecting the second capacitor 106 to the circuit.

Thus, an exemplary configuration of the non-contact IC card practiced asthe first embodiment of the invention has been described. The followingdescribes a wireless communications method practiced as the firstembodiment of the invention.

FIG. 4A is a flowchart indicative of the wireless communications methodmentioned above. As shown, in this wireless communications method, apolling signal is transmitted from the reader/writer 150 through theantenna coil 152 (step S110). If the non-contact IC card 100 is in theproximity of the reader/writer 150, the non-contact IC card 100 receivesthe polling signal through the antenna coil 102 (step S120).

Receiving the polling signal from the reader/writer 150, the non-contactIC card 100 causes the confirmation block 123 to check whether apredetermined period of time has passed since the reception of thepolling signal (step S130). If the predetermined period of time is foundnot passed by the confirmation block 123, then the non-contact IC card100 transmits, through the antenna coil 102, a response signal to thepolling signal received from the reader/writer 150 (step S150).

Here, it is determined whether the reader/writer 150 is successful inthe reception of the response signal from the non-contact IC card 100(step S160). If the reader/writer 150 is found successful in thereception of the response signal, namely, if the resistor 107 of thenon-contact IC card 100 is made valid to change the voltage across theantenna coil 152, the communication continues (step S170). However, ifthe resistor 107 is made valid but there occurs no change in the voltageacross the antenna coil 152, then the reader/writer 150 determined thatthe reception of the response signal from the non-contact IC card 100has failed, upon which the procedure returns to step S110 to transmit apolling signal again.

On the other hand, if the predetermined period of time is found passedsince the reception of the polling signal in step S130, then theresonance frequency of the non-contact IC card 100 is changed (stepS140). To be more specific, the digital circuit 120 outputs a signal toturn on the switches 112 a and 112 b to connect the second capacitor 106to the circuit. Connecting the second capacitor 106 to the circuit addsthe second capacitor 106 to the resonance circuit made up of the antennacoil 102 and first capacitor 104. Let the inductance of the antenna coil102 be L, the capacitance of the first capacitor 104 be C1, and thecapacitance of the second capacitor 106 be C2, then the resonancefrequency changes from ½π(L×C1)^(1/2) to ½π{L×(C1+C2)}^(1/2).

FIG. 5 shows a relationship between the capacitance of the non-contactIC card and the voltage value of the reader/writer (R/W). FIG. 5A showsa relationship between the capacitance of the non-contact IC card andthe voltage value of the reader/writer when the distance between thenon-contact IC card 100 and the reader/writer 150 is 10 mm. In thefigure, the dashed line is indicative of a case in which the resistor107 of the non-contact IC card 100 is invalid, while the solid line isindicative of a case in which the resistor 107 of the non-contact ICcard 100 is valid.

In the present embodiment, capacitance C1 of the first capacitor 104 is125 pF. Hence, if the distance between the non-contact IC card 100 andthe reader/writer 150 is 10 mm, for example, there is an obvious changein the value of a voltage generated across the antenna coil 152 of thereader/writer 150 when the resistor 107 is validated. Therefore, in thecase shown in FIG. 5A, the reader/writer 150 can receive a responsesignal from the non-contact IC card 100 when the resistor 107 isvalidated.

FIG. 5B shows a relationship between the capacitance of the non-contactIC card and the voltage value of reader/writer (R/W) when the distancebetween the non-contact IC card 100 and the reader/writer 150 is 6 mm.Like the relationship shown in FIG. 5A, the dashed line is indicative ofa case where the resistor 107 of the non-contact IC card 100 is invalid,while the solid line is indicative of a case where the resistor 107 ofthe non-contact IC card 100 is valid.

When the distance between the non-contact IC card 100 and thereader/writer 150 is 10 mm, there occurs little change in the value of avoltage generated across the antenna coil 152 of the reader/writer 150when the resistor 107 is validated. Therefore, in the case of FIG. 5B,the reader/writer 150 cannot receive a response signal from thenon-contact IC card 100 when the resistor 107 is validated, so that thereader/writer 150 repeatedly outputs a polling signal for thecommunication with the non-contact IC card 100.

The non-contact IC card 100 comes to repeatedly receive the pollingsignal from the reader/writer 150. Here, if the predetermined conditionhas been satisfied in the non-contact IC card 100, the capacitance ofthe non-contact IC card 100 is changed to change the resonancefrequency, thereby causing the reader/writer 150 to recognize a responseissued from the non-contact IC card 100. In the case of FIG. 5B,changing the capacitance of the non-contact IC card 100 from 125 pF to ahigher level or a lower level obviously changes the value of a voltagegenerated across the antenna coil 152 of the reader/writer 150 when theresistor 107 is validated. This obvious change allows the reader/writer150 to receive a response signal from the non-contact IC card 100 whenthe resistor 107 is validated.

In the present embodiment, the switches 112 a and 112 b are turned on toconnect the second capacitor 106 to the circuit in parallel, so that thecapacitance of the non-contact IC card 100 is changed higher than 125pF; however, the present invention is not limited to this configuration.For example, a signal may be entered in the switching block to separatethe capacitor from the resonance circuit and change the capacitance ofthe entire resonance circuit lower, thereby changing the resonancefrequency.

FIG. 5C shows a relationship between the capacitance of the non-contactIC card 100 and the voltage value of the reader/writer (R/W) when thedistance between the non-contact IC card 100 and the reader/writer 150is 4 mm. FIG. 5D shows a relationship between the capacitance of thenon-contact IC card 100 and the voltage value of the reader/writer (R/W)when the distance between the non-contact IC card 100 and thereader/writer 150 is 0 mm. Like the relationship shown in FIG. 5A, thedashed line is indicative of a case where the resistor 107 of thenon-contact IC card 100 is invalid, while the solid line is indicativeof a case where the resistor 107 of the non-contact IC card 100 isvalid.

If the distance between the non-contact IC card 100 and thereader/writer 150 is 4 mm, and if the capacitance of the non-contact ICcard 100 is 125 pF, an obvious change occurs in the value of a voltagegenerated across the antenna coil 152 of the reader/writer 150 when theresistor 107 is validated. However, if the distance is 0 mm, thereoccurs little change in the value of a voltage generated across theantenna coil 152.

As shown in FIG. 5D, if the distance is 0 mm, increasing thecapacitances of all capacitors of the non-contact IC card 100 does notalmost change the value of a voltage generated across the antenna coil152. However, when the capacitance of the capacitor of the non-contactIC card 100 is decreased, the reader/writer 150 can recognize a responsesignal from the non-contact IC card 100.

As described, changing the resonance frequency of the resonance circuitdepending upon when the a predetermined time has been reached as apredetermined condition allow the reader/writer terminal to recognize aresponse from the non-contact IC card.

It should be noted that, with the wireless communications method shownin FIG. 4A, the resonance frequency of the resonance circuit is changeddepending upon whether a predetermined time has been reached; it is alsopracticable to change the resonance frequency depending upon whether aresponse signal has been transmitted the predetermined number of timesas a predetermined condition.

FIG. 4B is a flowchart indicative of the wireless communications methodpracticed as the first embodiment of the invention. When thereader/writer 150 transmits a polling signal (step S110), thenon-contact IC card 100 receives this polling signal (step S120). Whenthe polling signal is received by the non-contact IC card 100, theresponse count is incremented by one (step S122). Then, the confirmationblock 123 checks on the basis of the increment whether the predeterminednumber of times the response has been made has been reached (step S132).

If the predetermined number of times is found not reached, namely, ifthe response has not been made three times for example, the responsesignal is transmitted to the reader/writer 150 as it is(step S150). Ifthe predetermined number of times is found reached, the resonancefrequency is changed (step S140) and the response signal is transmittedto the reader/writer 150 with the changed resonance frequency (stepS150). The reader/writer 150 determines whether the reception of theresponse signal from the non-contact IC card 100 is successful or not(step S160). If the reception is found successful, the communication iscontinued (step S170). If the reception is found failing, then theprocedure returns to step S110 to transmit a polling signal again.

As described, changing the resonance frequency of the resonance circuitdepending upon whether a response signal has been transmitted thepredetermined number of times as a predetermined condition also allowsthe reader/writer terminal to recognize a response from the non-contactIC terminal. Obviously, the number of times a response signal has beentransmitted is not limited to three times; for example, this conditionmay also be two or one time or four or more times for example in thepresent embodiment.

Thus, the wireless communications method practiced as the firstembodiment of the invention has been described.

It should be noted that the above-described wireless communicationsmethod may be executed by a computer program that is stored in thenon-contact IC card 100 and includes the processing of receiving a radiowave having a predetermined frequency and the processing of switchingbetween the capacitances of all capacitors through the switching block112.

As described above and according to the first embodiment of theinvention, changing the number of capacitor to be used to change theresonance frequency can improve the communication between thereader/writer terminal, the non-contact IC card, and the informationprocessing terminal.

A Second Embodiment

With reference to the above-described first embodiment, an integratedcircuit has been described in which the resonance frequency of theresonance circuit may be changed by increasing the number of capacitorsused. With reference to the second embodiment, the resonance frequencyof the resonance circuit is changed by increasing the number of windingsof coil.

Referring to FIG. 6, there is shown a circuit diagram illustrating anintegrated circuit practiced as the second embodiment of the invention.As shown, an integrated circuit 224 of the second embodiment is made upof an antenna coil 202, a capacitor 204, a resistor 207, and a switchingblock 212.

Like the antenna coil 102 of the first embodiment, receiving a radiowave containing a predetermined frequency component from a radio wavegenerating device such as a reader/writer terminal, the antenna coil 202generates an alternating voltage across the antenna coil 202 byelectromagnetic induction. In the second embodiment, an intermediateterminal is arranged between both the terminals of the antenna coil 202so as to change the inductance in multiple levels. This arrangement canchange the number of windings by switching between the end terminals andthe intermediate terminal. In the second embodiment, the number ofwindings of the 202 is, but not exclusively, five and the number ofwindings for the intermediate terminal is, but not exclusively, three.

Connecting the antenna coil 202 and the capacitor 204 in parallel asshown in FIG. 6 configures a resonance circuit. When a change occurs inthe magnetic field passing the antenna coil 202, an alternating voltageis generated on the antenna coil 202 and a current flows into theintegrated circuit 224 through the resistor 207, consuming the electricpower through the resistor 207.

The switching block 212 is turned on/off to change the number ofwindings of the antenna coil 202. Changing the number of windings of theantenna coil 202 changes the resonance frequency of the resonancecircuit made up of the antenna coil 202 and the capacitor 204.

The switching block 212 may be configured by including a plurality ofswitching elements. In the second embodiment, the switching element mayalso be a FET, a MOSFET for example. In the second embodiment, theswitching block 212 includes switches 212 a and 212 b.

As described before, in the first embodiment, the resonance frequency ofthe resonance circuit is changed by changing the capacitance of theresonance circuit by operating the switching block. In the secondembodiment, the inductance of the resonance circuit is changed byoperating the switching block, thereby changing the resonance frequencyof the resonance circuit.

Namely, the number of windings of the antenna coil is changed from threeto five by operating the switching block 212 to change the inductance ofthe antenna coil 202, thereby changing the resonance frequency of theresonance circuit.

Incorporating the integrated circuit 224 of the second embodiment intothe non-contact IC card of the first embodiment allows the reader/writerto recognize a response from the non-contact IC card by changing theresonance frequency if the reader/writer cannot otherwise recognize aresponse from the non-contact IC card.

It should be noted that the above-mentioned processing may be executedby a computer program that include the processing of receiving a radiowave having a predetermined frequency and the processing of switchingthe number of windings of the antenna coil 202 by operating theswitching block 212.

As described above and according to the second embodiment of theinvention, changing the inductance by changing the number of antennacoil windings to change the resonance frequency can improve thecommunication between the reader/writer terminal, the non-contact ICcard, and the information processing terminal.

A Third Embodiment

In the foregoing first and second embodiments, the resonance frequencyof a resonance circuit contained in a non-contact IC card or aninformation processing terminal is changed to improve the communicationbetween a reader/writer terminal and the non-contact IC card or theinformation processing terminal. In the third embodiment, the resonancefrequency of a resonance circuit contained in a reader/writer terminalis changed to improve the communication.

Referring to FIG. 7, there is shown a block diagram illustrating anexemplary configuration of a reader/writer terminal practiced as thethird embodiment of the invention. As shown in FIG. 7, a reader/writer350 practiced as the third embodiment is made up of an antenna coil 352,a first capacitor 354, a second capacitor 356, a switching block 358, atransmission block 360, a reception block 362, and a control block 364.

The antenna coil 352 transmits a radio wave outside and receives aresponse signal from the non-contact IC card 300. The antenna coil 352,the first capacitor 354, and the second capacitor 356 form a frequencyresonance circuit. The frequency resonance circuit passes a particularfrequency band (or a resonance frequency). Normally, the antenna coil352 and the first capacitor 354 form the frequency resonance circuit,the second capacitor 356 being separated from the circuit.

The switching block 358 is turned on/off to connect or disconnect thesecond capacitor 356 to and from the circuit. Connecting ordisconnecting the second capacitor 356 can change the resonancefrequency of the resonance circuit made up of the antenna coil 352 andthe first capacitor 354.

The transmission block 360 is configured by a signal carrier generatorand a modulator for modulating the signal carrier in accordance with theinformation to be transmitted, for example. The reception block 362 isconfigured by a detector for detecting the envelope of a signal receivedat the antenna coil 352 and a demodulator for demodulating the detectedsignal, for example. The control block 364 controls the reader/writer350 in its entirety.

Thus, the configuration of the reader/writer terminal associated withthe third embodiment of the invention has been described. The followingdescribes a wireless communications method practiced as the thirdembodiment with reference to FIG. 8.

Referring to FIG. 8, there is shown a flowchart indicative of thewireless communications method associated with the third embodiment.First, the reader/writer 350 outputs a polling signal through theantenna coil 352 (step S210). If there is a non-contact IC card 300 inthe proximity of the reader/writer 350, the non-contact IC card 300receives a polling signal from the reader/writer 350 (step S220). Uponreception of the polling signal, the non-contact IC card 300 returns aresponse signal to the reader/writer 350 (step S230).

The reader/writer 350 determines whether the reception of the responsesignal from the non-contact IC card 300 is successful or not (stepS240). If the reception is found failing, namely, if no change occurredin the voltage across the antenna coil 352 of the reader/writer 350,then the control block 364 of the reader/writer 350 determines whether apredetermined condition has been satisfied or not (step S250).

If the predetermined condition is found satisfied as a result of thechecking by the control block 364, then the control block 364 transmitsa signal for turning on the switching block 358 to validate the secondcapacitor 356, thereby changing the resonance frequency of thereader/writer 350 (step S260). When the resonance frequency of thereader/writer 350 has been changed, the procedure returns to step S210to transmit a polling signal again. Then, if the communication with thenon-contact IC card 300 is successful with the changed resonancefrequency, the reader/writer 350 subsequently fixes the resonancefrequency to that changed frequency to continue the communication withthe non-contact IC card 300.

If the predetermined condition is found not satisfied in step S250, thenthe procedure returns to step S210 to transmit a polling signal again.

On the other hand, if the reception of a response signal from thenon-contact IC card 300 is found successful in step S240, then theresonance frequency is not changed and the communication is continued asit is.

Thus, changing the resonance frequency of the resonance circuitdepending upon whether a predetermined conditions has been satisfied onthe side of the reader/writer also allows the reader/writer terminal torecognize a response from the non-contact IC card.

It should be noted that the above-mentioned wireless communicationsmethod according to the third embodiment may be executed by a computerprogram that is stored in the reader/writer 350 and includes theprocessing of determining whether a predetermined condition has beensatisfied and the processing of validating the second capacitor 356 byoperating the switching block 358 to switch between the capacitances ofall capacitors, thereby changing the resonance frequency of theresonance circuit.

As described and according to the third embodiment of the invention, thenumber of capacitors for use in a reader/writer terminal is changed tochange the resonance frequency of a resonance circuit, thereby improvingthe communication between the reader/writer terminal and non-contact ICcard or an information processing terminal.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purpose only.It is obvious that changes and variations may be made by those skilledin the art without departing from the gist of claims. Therefore, thechanges and variations are understood to be contained in the spirit orscope of the claims that follow.

The embodiments of the present invention are applicable to an integratedcircuit, a non-contact IC card, a reader/writer, a wirelesscommunications method, and a computer program.

1. An integrated circuit configured to execute wireless communication byuse of a magnetic field, comprising: a resonance circuit havingresonance frequencies of a plurality of levels; a confirmation blockconfigured to confirm whether a predetermined condition is satisfied;and a switching block configured to change said resonance frequencies ifsaid predetermined condition is found satisfied as a result of theconfirmation.
 2. The integrated circuit according to claim 1, whereinsaid predetermined condition is a predetermined count executed in saidconfirmation block.
 3. The integrated circuit according to claim 1,wherein said predetermined condition is a predetermined period of timemeasured in said confirmation block.
 4. The integrated circuit accordingto claim 1, further comprising a capacitor having capacitances of aplurality of levels, said switching block switching between saidcapacitances to change said resonance frequencies.
 5. The integratedcircuit according to claim 1, further comprising an inductor havinginductances of a plurality of levels, said switching block switchingbetween said inductances to change said resonance frequencies.
 6. Anon-contact integrated circuit card comprising an integrated circuit asset forth in claim
 1. 7. An information processing terminal comprisingan integrated circuit as set forth in claim
 1. 8. A card reader/writercomprising an integrated circuit as set forth in claim
 1. 9. A wirelesscommunications method based on an integrated circuit having a resonancecircuit having resonance frequencies of a plurality of levels,comprising the steps of: confirming whether a predetermined conditionsis satisfied; and changing said resonance frequencies by switchingbetween said resonance frequencies if said predetermined condition isfound satisfied.
 10. A computer program configured to control anintegrated circuit having resonance frequencies of a plurality oflevels, comprising the processes of: confirming whether a predeterminedconditions is satisfied; and changing said resonance frequencies byswitching between said resonance frequencies if said predeterminedcondition is found satisfied.